Method B: x = a(x'+ vt') and t = a(t'+ vx'/c^2) are the Lorentz
transformations from the ship frame to the earth frame. Let the tail of the
ship be at x'=0 at t'=0. and interpret the above equations as space and
time *intervals*. Accordingly set x' = 200 and t' = l/c, and solve for t.